The thinning of a substrate used in the aforementioned technical fields may be carried out, for example, by chemical etching.
When a substrate of semiconductor-on-insulator (SeOI) type is thinned, the chemical etching is relatively easy to use since the buried oxide layer serves as an etch stop layer. When it is a question of a solid substrate, the thinning is slightly more complex since it is then necessary to create an etch stop layer, for example, by p- or n-type doping of the solid substrate.
However, in the particular case where the donor substrate comprises a buried circuit layer, the chemical etching of the layer of material that covers the buried circuit layer becomes truly problematic. Specifically, the chemical solutions used (for example, sulfuric acid (H2SO4), phosphoric acid (H3PO4) or hydrofluoric acid (HF) in the case of the etching of silicon) are particularly aggressive with respect to metals and, therefore, with respect to the layer comprising the circuits.
This results in a lateral etching of the buried circuit layer, which may reach a centimeter or more from the edge. The BSI sensors manufactured in the vicinity of this damaged zone are then unusable.
A process is already known from European Pat. No. EP 1 962 325 (hereinafter the '325 patent) for manufacturing a bonded substrate, by transfer of layers, which comprises steps of producing a peripheral groove on the front side of a donor substrate, of thermal oxidation of this substrate, of bonding a receiver substrate to the front side and of thinning the donor substrate from its back side, until the bottom of the groove is reached.
Such a process makes it possible to transfer to the receiver substrate only the central portion of the donor substrate and to remove the poorly bonded peripheral portion thereof.
However, the '325 patent absolutely does not describe the treatment of donor substrates comprising a buried circuit layer and, furthermore, such a layer would not withstand the thermal oxidation carried out, or the thermal treatment after bonding at more than 1000° C., which are described in the '325 patent.
The objective of the disclosure is, therefore, to propose a process for transferring a buried circuit layer that resolves the aforementioned drawbacks of the prior art and, in particular, that avoids damaging these circuits.
For this purpose, the disclosure relates to a process for transferring a buried circuit layer (2).
In accordance with the disclosure, this process comprises the following steps:                taking a donor substrate internally comprising an etch stop zone and covered on one of its sides, referred to as the “front” side, with a circuit layer,        producing over the entire circumference of the donor substrate, on its side covered with the circuit layer, either a peripheral trench that extends at a distance from the lateral edge of the donor substrate, or a peripheral routing, the routing or trench being produced over a depth such that they pass entirely through the circuit layer and extend into the donor substrate,        depositing on the exposed side of the circuit layer and on the routed side or on the walls of the trench, a layer of a stop material that is selective with respect to the etching of the circuit layer, referred to as a “second stop layer,” without filling the trench,        bonding a receiver substrate to the donor substrate on the side covered by the second stop layer,        thinning the donor substrate (1) by chemical etching of its back side, until the etch stop zone is reached, so as to obtain the transfer of the buried circuit layer to the receiver substrate.        
According to other advantageous and nonlimiting features of the disclosure, taken alone or in combination:                the etch stop zone is a layer, referred to as a “first stop layer,” of a material that is selective with respect to the etching of the material of the back portion of the donor substrate;        the etch stop zone is an interface between a doped front layer and a non-doped back layer of the donor substrate;        the peripheral routing or the peripheral trench has a depth such that it passes through the etch stop zone, without penetrating into the back portion or the back layer of the donor substrate;        the peripheral routing or the peripheral trench is produced over a depth such that it does not pass through the etch stop zone and in that, after the chemical etching thinning step, an additional step of mechanical removal of the residual peripheral ring of the donor substrate is carried out, in particular, by grinding or chemical mechanical polishing (CMP);        the peripheral routing or the peripheral trench has a depth such that it passes through the etch stop zone and extends into the back portion or the back layer of the donor substrate and, after the chemical etching thinning step, an additional step of mechanical removal of the residue of the second stop layer is carried out, in particular, by grinding or chemical mechanical polishing (CMP);        the second stop layer is deposited by a technique selected from chemical vapor deposition (CVD) or spin coating;        the peripheral trench is produced with the aid of a technique selected from laser etching, dry etching and wet etching;        the peripheral trench is located at a distance from the lateral edge of the donor substrate of less than or equal to 5 mm;        the width of the trench is between 10 μm and 500 μm;        the materials forming the first and the second stop layer are selected from oxides or nitrides;        the materials forming the first and the second stop layer are selected from silicon oxide, silicon oxynitride or silicon oxycarbide;        the materials forming the first and the second stop layer are identical;        the donor substrate is produced from a semiconductor material;        the bonding of the donor and receiver substrates takes place by molecular adhesion.        